In German, you would say ‘Ich liebe dich auch’ to express ‘I love you too.’
The phrase breaks down as follows: ‘Ich’ means ‘I’, ‘liebe’ translates to ‘love’, ‘dich’ means ‘you’, and ‘auch’ means ‘too’ or ‘also’. So, when you want to reciprocate someone’s expression of love in German, this is the phrase to use.